Each harddisk is a computer and like every computer it has an operating system (microcode).
The microcode is located in a reserved area that is inaccessible for the user.
This operating system is loaded every time the harddisk is started.

The models of a harddisk have different versions of the mircocode (firmware version).
In the initialization area, there are, additionally to the microcode, the individual parameters of the harddisk.
These parameters (e.g. damages of the surface) are detected during the production of the harddisk during a test run that takes several hours, and
can be changed further during the life time of the harddisk.

Having a damaged microcode, the harddisk normally starts but is not or not sufficiently recognized by the BIOS
(e.g. without the serial number). There is no access to the data.

In case of microcode bugs, X Datenrettung offers the data recovery as a standard service.